Side chain

As a side chain is used in the organic chemistry, a substituent ( radical, abbreviated R ) denotes a main chain, or cyclic group, such as a short carbon chain ( alkyl group ), which branches off from a long carbon chain or ring.

Side-chain alkanes at

Even with simple hydrocarbons side chains ( respectively the total degree of branching ) can be decisive for the molecule. Isooctane is particularly anti-knock in spark ignition engines, cetane in diesel engines particularly zündwillig.

Side chains in aromatics

A special feature have side chains in the chemistry of aromatic compounds. The hydrogen atoms on the carbon atom adjacent to the aromatic compounds are characterized by a specific reactivity towards radicals from (slight formation of the resonance stabilized benzyl radical ). They can be substituted, for example by chlorine (see benzyl ), or by oxygen ( Hock phenol synthesis by, cumene hydroperoxide method, phenol as the starting material for the plastic of polyamide 6, ε -caprolactam ).

The substitution in the side chains of aromatic compounds is carried out according to the SSS - rule, such as through the Seitenkettenhalogenierung in which a hydrogen atom of the side chain is replaced by a halogen atom. Alternatively, if a substitution reaction at the aromatic core and at the same time should be avoided in the side chain, the reaction according to the CCC rule must be performed.

Side chains in amino acids

Of great importance also have side chains in the amino acids. All proteinogenous amino acids are derived from glycine, in which a hydrogen atom (specifically the pro -S) in each case is replaced by a characteristic group. The rest may be a simple alkyl substituent (in the case of alanine, optionally branched as leucine ), but also other functional groups (such as hydroxy ( serine ), amino (for proline), thio ( in cysteine) and / or carboxy groups ( for aspartic acid) ). Also, aromatic and heteroaromatic compounds can be incorporated into the side chain ( tryptophan).

For simple main chains, the side chain is dominant for the structural characteristics ( basic amino (for proline), acidic amino acids (for aspartic acid) ).

Side chains in organic polymers

By modification of the side chains of polymers their properties can be manipulated. For X = H we obtain the non-polar polyethylene; for X = -COOH leads to the super- absorbers, a class of compounds with extremely hydrophilic properties. The relative disposition of the side chains play an important role in the tacticity of a polymer affects its properties and.

Side chains of inorganic polymers

Also in inorganic polymers can be installed side-chains. Silica gels are esterified with organic radicals. The polarity of the silica gels can be varied from highly polar to very nonpolar. These products are widely used in high performance liquid chromatography (HPLC ), especially in the reversed-phase chromatography.